The present invention relates to a semiconductor active electrostatic device. More particularly, the invention relates to an electro-mechanical converter or an electrostatic actuator utilizing an impurity semiconductor material as an active element effective to generate an electrostatic force when an external electrostatic field exceeds a given threshold to produce a drive torque.
The impurity semiconductor material has useful electrical characteristics specific to behavior of donor electrons or acceptor holes, and is utilized for various electronic components. For example, the Rectifying function of PN junction is utilized in diodes and bipolar transistors. Channel inversion is utilized in insulated gate transistors of the field effect type, which are integrated to form an MOSIC. Further, the piezoelectric effect of the semiconductor material is utilized in mechanical sensors, and the photoelectric effect is utilized in optical sensors. Moreover, the photoelectric effect is utilized in solar cells. In such a manner, research and development of the semiconductor device is conventionally associated to those of logic or intelligence elements, sensor elements and energy elements.
Recently, a mechanical effect has been found as the fourth function of the semiconductor material. In the field of micromachine engineering, an impurity semiconductor material is utilized as a rotor to constitute a semiconductor electrostatic motor. Such a motor is disclosed, for example, in U.S. Pat. No. 5,001,381. The semiconductor electrostatic motor operates in a manner such that an electrostatic field is applied to localize majority carriers contained in the impurity semiconductor of the rotor to thereby generate Coulomb force to obtain rotational drive torque.
The semiconductor electrostatic motor is a significant actuator based on discovery of the mechanical effect of the impurity semiconductor material. In addition to the intelligence function, sensing function and energy source function, the discovery of the mechanical function leads to construction of self-reliant robots or micromachines solely composed of semiconductor material. However, the known semiconductor electrostatic motor is capable of a rather primitive actuator simply responsive to an applied voltage to produce a drive torque. This motor has a rather limited application as an actuator, and is practically utilized only as a drive source. Such a primitive type of actuator lacks sophisticated functions such as a judgement or logic property, information processing property and intelligent property. Therefore, the actuator must be coupled to an external controller such as a computer in order to perform more sophisticated operations.